Tokkai Hei 8-340663 published by the Japanese Patent Office in 1996 discloses a motor/generator comprising two rotors and one stator coaxially arranged in three layers wherein one of the rotors is driven as a motor and the other is driven as a generator.
In this motor/generator, wo sets of coils are installed in the stator for providing a magnetic field for respective rotors, and two sets of inverters, i.e., current controllers, are provided for controlling respective sets of coils.